C4d Antibody (Monoclonal - neoantigen)

Activation of the classical complement pathway begins with binding of an activating substance (e.g. immune complex) to the C1q molecule of C1. This, in turn, activates the C1r (2) C1s (2) sub-units, resulting in cleavage of C4 to C4b near the amino terminus of the gamma chain releasing C4a in the process. The short-lived C4b molecule can bind covalently to membranes or other surfaces via either an amide or ester bond. This is an inefficient process that is limited to the immediate vicinity of the C1 complex. C4b then takes part in the classical convertase enzyme. Because of the short life of the C4b molecule much of the C4d is free and circulates in serum. Both bound and free C4b are strictly controlled in vivo. The ability of C4b to participate in classical pathway activation and opsonization reactions is inhibited by a single site cleavage of the alpha chain by Factor I. This reaction requires either C4 binding protein or CR1 as a cofactor. This initial cleavage inactivates C4b resulting in iC4b. Further degradation of this molecule by Factor I produces the C4c and C4d fragments. Both of these fragments can be produced in fluid phase or on target surface.

This monoclonal antibody was raised against purified human C4. It is specific for a neo-antigen expressed on the C4d domain of C4 and therefore reactive to all C4d-containing fragments of C4, but not with C4 itself.